'A big scam company just stole my whole game': A Backrooms indie dev has been forced to seek legal help after someone took their game off Steam and uploaded it to the Nintendo Store

My first thought was maybe they had some way to decompile games from a specific engine but the two other games mentioned are different engines, Unity and Unreal. So either they have methods for both of those two which isn't that outlandish since they're both popular enough for people to find a way to do that or they have some other method to port it over. But since the article mentioned they changed some things in the game my bet is on the decompiling.